Macroevolution





  • Microevolution happens at the population level (natural selection, genetic drift, gene flow)


  • Macroevolution: Speciation events form evolutionary independent populations


  • New species are the bridge between evolution within a population and larger patterns in evolution, such as new taxonomic groups

How/Why species form: The limits of human cognition

What actually is a “Species”?







  • Textbooks: A group of populations whose members have the potential to interbreed in nature and produce viable offspring

What actually is a “Species”?







  • Textbooks: A group of populations whose members have the potential to interbreed in nature and produce viable offspring

Biological Species Concept: Unity of reproduction


  • Reproductive isolation between populations results in a lack of gene flow
    • what are the consequences of no gene flow?


  • Individuals do not interbred with other populations or are unable to produce viable offspring after mating
    • via pre- and post-zygotic barriers


  • BSC: Members of a biological speci es are united by the potential ability to be reproductively compatible

Mechanisms of reproductive isolation in Meadowlarks


Issues with the biological species concept



  • How do we effectively evaluate isolation?
    • Is this even possible in fossils?


  • Geographic proximity: how do we know if they cant make babies?


  • Asexual reproduction is unaccounted for…
    • Belloid rotifers haven’t reproduced sexually for > 80 million years
    • An estimated 2000 species of asexual rotifers are known

Morphological Species Concept: Unity of body plans

MSC: defines a species based on groups of physical traits that are unique to each species
MSC: no issues with fossils or reproductive type

Issues with the morphological species concept




  • Applies to all organisms but…. what kinds of traits & how many?
    • Subjective to the scientist!


  • Species can change their form: Polymorphisms


  • Cryptic species that do not differ in morphology
    • lots of mimics in nature!

Lineage Species Concept: Unity of ancestry

LSC uses genetic similarity/differences based on ancestry to determine species but is subjective in the magnitude of differences needed.

How new species arise: Allopatry

Allopatric speciation in Hawaiian fruit flies

Hawaiian islands form through time. Fruit flies from one population migrate to a new island (physical separation) and have formed many new species.

How new species arise: Sympatry

Sympatry in Hawthorn and apple flies

Study aid: The geography of speciation

The pre- and postzygotic barriers can form for either type of speciation